Lighting systems for hallways often include a plurality of spaced lamps which are connected to a primary power source. In such cases, when the primary power source fails a back up battery powered emergency system is operated. Such systems include separately wired spot lights located in a position to provide a low level illumination in the hall for evacuation. In some cases the spot lights are located such that smoke pouring from one location could obscure the light and unnecessarily reduce the level of the hall illumination.
An alternative is to provide a downlighting system including a plurality of spaced low voltage lamps along the length of the hall to provide a softened lighting effect in the hallway under normal lighting conditions. Such lighting systems are set-forth in U.S. Pat. Nos. 4,890,200 and 5,003,432 issued to the inventor of the present invention. While suitable for their intended purpose, such lighting systems included a relay switch that connected the small dedicated lamps to an emergency battery power source when the primary power failed through a circuit network including the secondary winding of a step down transformer that powered the normal illumination lamps during operation of the primary power source.
Using the same lamps for both normal and emergency illumination, the illumination of the hallway under emergency conditions would be reduced undesirably unless the emergency battery were selected to have a voltage approaching that of the voltage across the secondary winding. Batteries with such voltage ratings and of the rechargeable type as required for low maintenance have a high initial cost which in the case of multiple installations in commercial buildings is prohibitive when compared to existing emergency lighting systems of the spot light type.